My 10 year old sister got caught sending nudes

Earlier today I decided to go through my sisters phone who is 10 I am (16) I noticed an account she was talking to on instagram called "issabadbitch" well as I went into the messages the person initially asked her to be her "girlfriend" so my sister is going with it saying she'll be her girlfriend & etc asks this page that she knows NOTHING about if they want to see her private parts and to go first if so . She starts from her chest nude to her vagina showing her vagina in the video. I told my older sister asap and she took her phone my father told her it wasn't her fault and that she should not have an instagram my mother told us to spank her and take her phone. My mom does check her messages frequently she's only allowed to use it because she's on a dance team and they talk there .

My question is what should an appropriate punishment be ?